1. Field of the Invention
The present invention relates to an apparatus for detecting a residual quantity of a toner material contained in a container.
In an electrophotographic copying apparatus, toner contained in a developing device is consumed for every copying operation. Accordingly, it is usually necessary to provide a toner supply device for supplying or replinishing supplementary toner material to the developing device. To this end, the residual quantity of the toner material remaining within the toner supply device is constantly detected, whereby an alarm is produced for informing an operator of the need for additional loading of toner into the toner supply device when the residual toner quantity has decreased to a value below a predetermined level.
2. Description of the Prior Art
As a method of detecting the residual quantity of toner in the toner supply container, it has been hitherto known to measure the weight of toner with the aid of a micro-switch disposed at a bottom of the toner supply container or to detect the residual quantity of toner electrically by making use of the dielectric constant of the toner material.
However, the first mentioned detecting method is disadvantageous in that variation in weight of the toner can not be detected in a stable manner due to the fact that the toner material is inherently of very light weight. On the other hand, the second mentioned detecting method suffers from drawbacks in that a measuring apparatus of large size and complicated structure is required due to the low dielectric constant of the toner material. In brief, the hitherto known detecting methods are disadvantageous in having low sensitivity, poor stability and a degraded reliability.